MCSA (Motor Current Signature Analysis ) for 6 kV motors

[iphapppi]

My Company wants to buy MCSA (Motor Current Signature Analysis) for our PdM (Predictive Maintenance)System. I'm really a beginner about this MCSA, I only know that it can detect any malfunction inside a motor like broken rotor, eccentricity air gap etc. Basic on your experience, what's the difficulties of using this equipment, and also the advantages and weakness of using MCSA to the motor. is it suitable for our large motors like CWP, IDF, PAF etc(the motor is 6 kV)

 

[electricpete]

We have a very scaled down version of motor current signature analysis at our plant. We collect data using our Entek datapak vibration data collector, using a particular small clamp-on probe (instead of accelerometer) which plugs direclty into the datapak. We monitor the CT secondary lead at input to the panel meter (observing local electrical safety program). The data is saved and analysed using the same software that we use for vibration (E-monitor). For 480volt, it requires a larger clamp-on and a special converter box and (without ct's), tends to be harder to access safely... we don't routinely monitor 480vac.

For us, the sole purpose of this test for us is to detect/evaluate degrading rotor bar conditions. During my 12 years monitoring 30 13.2kv motors plus 60 4kv motors, we have detected or confirmed 3 rotor bar problems. Actually the two more severe problems were both detected by vibration/noise and confirmed by current signature. The one that was detected by current signature only was very early stage, not yet even at the point of affecting vibration or noise, one could argue not a big problem. I do have somewhat of a case study on that one posted on maintenanceforums.com

We do the test once every 1 to 3 years depending on application, and when some other unusual symptoms pop up. Actually come to think of it, it has been a handy tool to "rule out" rotor bar problems in a number of other scenario's investigating abnormal vibration (in addition to the three mentioned above).

Some of the systems offered also monitor voltage.... I tend to think the extra effort and risk involved in hooking up to monitor voltage is not worth it. The extra information gained is minimal.

It may be useful if the box you're looking at has the capability to monitor current time waveform during starting... particularly when trying to figure out tripss during start. Although you should be aware that is not a straightforward evaluation to consider the errors of your instrumentation, the way your protection responds to non-sinusoidal starting waveform etc. And in the end it often turns out to be more of an empircal excercize than an analytical excercize (particularly troubleshooting instantaneous trips of molded case circuit breakers).

The bottom line, I tend to think it's a waste of money to buy an expensive tester and software. The effort and expense to add these things in conjunction with your vib monitoring program is much less. That's just one opinion colored by my own experiences, others may differ.

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